Try looking in the registry editor under HKEY_LOCAL_MACHINE,then scroll down to Software, then to CLASSES, then to Microsoft,then to Windows (folder icon),scroll down to (near the bottom) "Run,Run-,RunOnce,RunOnceEx,RunServices,RunServices-,RunServicesOnce and Setup" These folders in quotes can contain spyware or viruses and boot up when your computer is turned on.
Try using the System File Checker to see if it detects that the system file is corrupted:Go to Start->Run and type in sfc /scannow and hit OK (note: there is a space between sfc and /). Leave it on the first option and let it scan. If it finds any files missing/corrupted, it may ask for the Windows CD.
You can allso go to start,then run and type msconfig.exe and click on the right tab to see anything unusual,thats booting up.
On this computer that Im running Windows Vista, Im not exactley sure how to get to the start\ run feature,maybe someone can clear that up,on xp is alot easyer.
I allso recomend the program called win rescue,it will back up your registry and help prevent this from happening again.
some tool are found here.http://www.greyknight17.com/download.php
Google this:Kill startup programshttp://technet.microsoft.co...ernals/bb963902.aspxhttp://ask.metafilter.com/9...l-autostart-programs